1. Field of the Invention
The present invention relates to a liquid crystal display device and the like for dynamically changing a display frame rate in accordance with an inputted frame rate (referred to as fps (Frames Per Second) hereinafter. In the current Specification, referring to a case of a given structural element A, an incident where a signal B enters to the structural element A is expressed as “the structural element A inputs the signal B” and an incident B where a signal C exits from the structural element A is expressed as “the structural element A outputs the signal C”.
2. Description of the Related Art
Typical liquid crystal display devices follow the stream of the old CRT (Cathode Ray Tube) display and are driven mainly with fixed fps of 60 Hz.
In the meantime, moving pictures of video games and the like are generated by rendering processing of a host processor (mainly GPU (Graphic Processor Unit). The frame rate (fps) of the moving picture data outputted to a liquid crystal display device every time the rendering processing is completed is not fixed but dynamically changes and also may be synchronized with operations of an end user in some cases.
FIG. 21 is a block diagram showing structures of a typical liquid crystal display device which shows moving pictures of video games and the periphery thereof. In FIG. 21, a GPU 102 generates image data 102a for displaying a video game by using rendering processing. Further, the GPU 102 may perform rendering processing that is synchronized with an operation signal 101a of an end user. Note that fps of the rendering processing is not fixed but changes dynamically. A display controller 103 is a signal processing device for writing image data to a liquid crystal panel, and outputs image data 103a towards the liquid crystal panel 104 at fixed fps of 60 Hz. An example of the display controller 103 is a signal processing circuit including a timing controller and a power supply circuit. The liquid crystal panel 104 displays the image data 103a inputted from the display controller 103 as a moving picture, and it also includes a driver component and the like. An example of the liquid crystal panel 104 is a TFT panel to which a source driver and a gate driver are mounted. The liquid crystal display device 100 includes the display controller 103 and the liquid crystal panel 104.
When the image data 102a of dynamically changing fps is transformed to the image data 103a of fixed fps and it is displayed on the liquid crystal panel 104, failures as in (1), (2), and (3) described below are generated due to the shift between the both kinds of fps. Such failures are perceived as discomfort by an end user 101.
(1) What is called “jerkiness” of moving pictures. It is a phenomenon where moving pictures are unable to be displayed smoothly due to generation of frame skipping when the display speed of input images is faster than the display speed of output images.
(2) Frame tearing. It is a phenomenon where images are viewed by being distorted or flickered when a plurality of screens of more than two are displayed within a display period of one screen.
(3) Time lag between a user operation and display. It is a delay of time from the point where the user does an operation to the point where an image is displayed on a liquid crystal panel.
A liquid crystal display device (referred to as “Related Technique 1” hereinafter) to which a measure for such failures is applied has already been on the market (Product Name NVIDIA G-SYNC, searched on Nov. 11, 2014 (URL:http://www.nvidia.com.jp/object/how-does-g-sync-work-jp.html) (Non-Patent Document 1)). Compared to normal liquid crystal display devices, the number of components used in Related Technique 1 is larger so that the cost is increased as well. Specifically, compared to the normal liquid crystal display devices, Related Technique 1 requires a larger-scale FPGA (Field Programmable Gate Array) and three memories so that the price thereof becomes higher by about 15,000 yen.
As a technique for suppressing the above-described failures other than Related Technique 1, there is considered a technique for dynamically changing fps for display also in accordance with inputted fps (referred to as “Related Technique 2” hereinafter). However, deviation of the charging polarities to the liquid crystal panel is an issue in the case of Related Technique 2.
That is, a normal liquid crystal panel is driven by inverting the writing polarity by each frame for preventing ghosting that is caused by deviation of the charging polarities. However, Related Technique 2 displays frames of different kinds of fps, so that charging time for the liquid crystal panel varies by each frame. Thus, even when the polarity is inverted for each frame, there is still an issue of deviation generated in the charging polarity characteristic.
Other related techniques are: Japanese Unexamined Patent Publication Hei 7-175443 (Active Matrix Type Liquid Crystal Display Device Driving method) (Patent Document 1); Japanese Unexamined Patent Publication 2014-32396 (Display Device Driving Method and Display Device) (Patent Document 2); Japanese Unexamined Patent Publication 2014-32399 (Liquid Crystal Display Device) (Patent Document 3); and Japanese Unexamined Patent Publication 2014-52623 (Liquid Crystal Display Device and Driving Method Thereof) (Patent Document 4).
Patent Document 1 discloses a double-speed driving technique for writing data with twice the fps of the data input in order to suppress ghosting of the liquid crystal panel generated by the display patterns. This technique requires a “field memory” for temporarily saving image data, a “control circuit” for controlling it, and a “synchronizing/separating circuit” for generating synchronizing signals used for driving the “control circuit”.
Patent Documents 2 to 4 disclose a technique including a feature of performing drive by lowering the polarity inversion rate in order to suppress the power consumption when performing high-fps drive. This technique requires a “counter” for detecting the synchronizing signals and counting the number thereof.
With respect to Related Technique 2 described above, deviation of the polarity is decreased by employing the technique such as the one disclosed in Patent Document 1 with which writing to the liquid crystal panel is performed at a double-speed with respect to the speed of input fps.
However, Patent Document 1 requires the structures for making it possible to store image data to a memory and to perform separation of synchronizing signals and for controlling those, which results in increasing the circuit scale and the cost. Further, through processing the image data at a double-speed, inverting the polarities at a double-speed, and using a memory device, the power consumption is increased. That is, the demands for decreasing the thickness of the liquid crystal display device as well as the price thereof (i.e., simplifying the structures) and lowering the power consumption are not satisfied with such solving means.
Patent Documents 2 to 4 present techniques for suppressing the power consumed by inverting the polarities with high-fps drive. Thus, when the techniques of Patent Documents 2 to 4 are combined with the technique of Patent Document 1, the power consumed by inverting the polarities at a double-speed can be suppressed. However, the power consumed by loading the memory device and performing image data processing becomes increased, so that the power consumption is increased as a whole.